A Bugg's tale of Yamahas and hand grenades

[gofishin]

...I still can't work out why the sudden "bang" theory is being promoted for an under propped motor.

It's probably more like an undetected gradual and 'cumulative' progression towards 'a bang' Sam.

If torque curves were available for outboards it would help, but then we would also need load curves for 'the particular' boat too, and these would obviously change a bit with different motor weights and boat loads etc.

Testing back-to-back good and bad/too big props you can actually easily hear the 'groan' from the motor under protest.

What's more, a prop can reach WOT but still be 'too big' in the low to mid-range if it has too much blade area for the motor torque produced at low revs. Been there, done that, and you could easily hear the 'motor protest' too. That prop only lasted one quick test!
Cheers
Brendon

Sent from my iPhone using Tapatalk

[fishing111]

Recently had a impeller replaced at Dolphin marine and while the mechanic was a nice enough bloke when I got home I found that my speed pick-up tube was just hanging off broken at the base. Now I don't use the old analogue speedo but it annoys me that things like that happen to which your not even made aware of, all of which doesn't bode well for repeat business.

[Bremic]

I have wondered about the effect of not using a boat regularly and breakdowns. Whilst we would like to think we will be using them often, work, life and weather dictate that most of us don't get out as often as we want. Corrosion is a factor in many repairs, parts replacement. A motor sitting idle is likely to have corrosion take a greater hold than one used regularly. If I parked my car up and didn't drive it for 6 months, I would be wondering if everything was going to run as well as it should, seals leaking etc.

[Owen]

Can't really see how under propping to the samll extent mentioned here can be blamed for terminal detonation given the type of use.
If the thing was trolling then it's operating as a displacement hull at low revs. Highly unlikely to be detonating in this condition.
Likewise once on the plane, the risk of detonation is low because there's little load.
If it spent all it's time at a speed where it couldn't quite make the plane then maybe, but in normal use the time spent in this mode would be a few seconds at most unless on trips the boat is loaded to the hilt.
In my mind the underpropping mentioned here would do little more than cause more fuel burn than necessary for the given speed.

One of conditions that leads to detonation is over heating, which was mentioned in the very first post.

I would have thought with todays electronics the timing and mixture would be adjusted immediately if detonation was detected.
That leads me to suspect the ECU / timing curve etc. and the operating temperature.
In the quest for maximum horespower from the lightest possible engine there is possibly no room for this intermediate load condition, or the knock and/or temp sensors didn't work.
In my opinion, that's the manufacturers fault as no matter what prop setup there is going to be a speed/revs combination with any boat that is going to have the motor working hard.
Be interesting to see the torque curve for this engine.

[patrol50]

Scotty - both motors are fed from different tanks with their own water separator. The fuel does sit from time to time with no use but for that trip there was 760l of new fuel on board. It was 98 octane. I only use 98 unless it's unavailable where I'll use 95. 91 has never been it in to my knowledge.
Haven't actually touched the cat yet - both myself and the mechanic are a touch busy and we're waiting for bit more time to delve right into the diagnosis

just a interested query - in the past I have been told both 98 and 95 octane fuel has a significant percentage of unadvised / unpublicised ethanol in it (as just under the designated 10 % content ) and allegedly with BP and others majors in particular - my local Caltex guy says there is no ethnol in the Caltex 91 fuel - not sure about there 95 and 98 so I do stick with the 91 Caltex brand fuel in my merc 4s 60 hp big foot - hate ethanol and the risk it poses to a OB and the fuel lines etc

any other informed comments re for or against that ??

cheers rob

[Dan5]

Achieving WOT while loaded is important it's like getting the diff ratio right IMO......easier on the motor and being able to rev freely..........When I had the 140 Suzy fitted to my last boat my self and the dealer did water tests with a few different props to achieve this.........their main concern was actually gearbox loading than engine under rev.......When talking to them about it they said both are important but a lot of others disreguard the stresses being put on the gearbox and mainly focus on the powerhead his opinion was they were as important as each other.

Dan

[Noelm]

Most newer motors will not be affected by ethanol in any way, same goes for fuel lines rubber gaskets and stuff, anything near on 8 years old is fine, some older equipment can be a drama though.

[Dan5]

Most newer motors will not be affected by ethanol in any way, same goes for fuel lines rubber gaskets and stuff, anything near on 8 years old is fine, some older equipment can be a drama though.

The Yamaha website actually states a 10% ethanol blend as being acceptable.
Prefer not to use it my self but I proberbly already have without even knowing it........

Dan

[Dignity]

Can't really see how under propping to the samll extent mentioned here can be blamed for terminal detonation given the type of use.
If the thing was trolling then it's operating as a displacement hull at low revs. Highly unlikely to be detonating in this condition.
Likewise once on the plane, the risk of detonation is low because there's little load.
If it spent all it's time at a speed where it couldn't quite make the plane then maybe, but in normal use the time spent in this mode would be a few seconds at most unless on trips the boat is loaded to the hilt.
In my mind the underpropping mentioned here would do little more than cause more fuel burn than necessary for the given speed.

One of conditions that leads to detonation is over heating, which was mentioned in the very first post.

I would have thought with todays electronics the timing and mixture would be adjusted immediately if detonation was detected.
That leads me to suspect the ECU / timing curve etc. and the operating temperature.
In the quest for maximum horespower from the lightest possible engine there is possibly no room for this intermediate load condition, or the knock and/or temp sensors didn't work.
In my opinion, that's the manufacturers fault as no matter what prop setup there is going to be a speed/revs combination with any boat that is going to have the motor working hard.
Be interesting to see the torque curve for this engine.

It would be interesting what caused the overheating, in my recent case with a failed fuel injector my mechanic said there was little chance of it happening even though I operated it for over 3 hours as though there was some fuel getting through the yammies are drip fed the oil independently and the cylinder was still lubricated unlike some motors where the oil and fuel is mixed prior to firing, in that case the cylinder would have overheated. I still have not seen anything that shows that under propping a motor will cause it to overheat and cause the failure bugman has. I will eat very humble pie if I am proven wrong.

[bonneville]

Can't really see how under propping to the samll extent mentioned here can be blamed for terminal detonation given the type of use.
If the thing was trolling then it's operating as a displacement hull at low revs. Highly unlikely to be detonating in this condition.
Likewise once on the plane, the risk of detonation is low because there's little load.
If it spent all it's time at a speed where it couldn't quite make the plane then maybe, but in normal use the time spent in this mode would be a few seconds at most unless on trips the boat is loaded to the hilt.
In my mind the underpropping mentioned here would do little more than cause more fuel burn than necessary for the given speed.

One of conditions that leads to detonation is over heating, which was mentioned in the very first post.

I would have thought with todays electronics the timing and mixture would be adjusted immediately if detonation was detected.
That leads me to suspect the ECU / timing curve etc. and the operating temperature.
In the quest for maximum horespower from the lightest possible engine there is possibly no room for this intermediate load condition, or the knock and/or temp sensors didn't work.
In my opinion, that's the manufacturers fault as no matter what prop setup there is going to be a speed/revs combination with any boat that is going to have the motor working hard.
Be interesting to see the torque curve for this engine.

for the longevity of the motor, over propping is not good for the motor ! wont detonate the minute you do it, but will shorten the life of an engine if continued, I believe the engines in question had some hours on them.
that's why engine manufacturers state max rpm, if your not closely achieving that, the engine is not running at its optimum with regard to load. the relationship to the electronic or fuel mixtures plays apart but doesn't have anything to do with the effect under propping has on an engine. probably a good comparison would be taking 3rd and 4th gear away from a car, so you only had 1st, 2nd and 5th, driving in 5th gear at low speeds will make the engine labour, not good for an engine. probably not a great comparison. But if an engine is significantly under propped, there's no liability from the manufacturer.
from memory it was about a 1000 rev's under manufacturers spec's, that's quite a bit, which would indicate severe over propping.

but I guess until the engine is properly diagnosed we are all surmising, will be interesting to read the outcome...


regards
bonneville

[Noelm]

I think you mean over propped??

[bonneville]

I think you mean over propped??

LOL
beg mine,
doing to many things at once here.................

[The Black Unicorn]

Full Throttle RPM Range

5000 - 6000!!

This is off the engine specs. Surely if you are within this range then the engine should be fine. Why would they put it in their specs? If they required it to be in the high end of that range why wouldn't they state 5500-6000?

[Still_Dreamin]

I think you are all missing the real problem here.
HE HAS TOO MANY BOATS!!!!

[StevenM]

I think you are all missing the real problem here.
HE HAS TOO MANY BOATS!!!!

Funny but not true

true an you really have too many boats?